# For HTML5-capable browsers, file uploads happen through a series of requests.
# 
# 1. Client tells server that one or more files are about to be uploaded; the
#    server responds with a "job ID" that the client should use for the rest of
#    the upload.
#    
# 2. For each file (sequentially):
#    a. Client tells server the name, size, and type of the file.
#    b. Client sends server a small-ish blob of data.
#    c. Repeat 2b until the entire file has been uploaded.
#    d. Client tells server that the current file is done.
#    
# 3. Repeat 2 until all files have been uploaded.
# 
# 4. Client tells server that all files have been uploaded, along with the
#    input ID that this data should be associated with.
# 
# Unfortunately this approach will not work for browsers that don't support
# HTML5 File API, but the fallback approach we would like to use (multipart
# form upload, i.e. traditional HTTP POST-based file upload) doesn't work with
# the websockets package's HTTP server at the moment.

FileUploadOperation <- setRefClass(
  'FileUploadOperation',
  fields = list(
    .parent = 'ANY',
    .id = 'character',
    .files = 'data.frame',
    .dir = 'character',
    .currentFileInfo = 'list',
    .currentFileData = 'ANY'
  ),
  methods = list(
    initialize = function(parent, id, dir) {
      .parent <<- parent
      .id <<- id
      .dir <<- dir
    },
    fileBegin = function(file) {
      .currentFileInfo <<- file

      filename <- file.path(.dir, as.character(length(.files)))
      row <- data.frame(name=file$name, size=file$size, type=file$type,
                        datapath=filename, stringsAsFactors=FALSE)
      
      if (length(.files) == 0)
        .files <<- row
      else
        .files <<- rbind(.files, row)
      
      .currentFileData <<- file(filename, open='wb')
    },
    fileChunk = function(rawdata) {
      writeBin(rawdata, .currentFileData)
    },
    fileEnd = function() {
      close(.currentFileData)
    },
    finish = function() {
      .parent$onJobFinished(.id)
      return(.files)
    }
  )
)

FileUploadContext <- setRefClass(
  'FileUploadContext',
  fields = list(
    .basedir = 'character',
    .operations = 'Map'
  ),
  methods = list(
    initialize = function(dir=tempdir()) {
      .basedir <<- dir
    },
    createUploadOperation = function() {
      while (TRUE) {
        id <- paste(as.raw(runif(12, min=0, max=0xFF)), collapse='')
        dir <- file.path(.basedir, id)
        if (!dir.create(dir))
          next
        
        op <- FileUploadOperation$new(.self, id, dir)
        .operations$set(id, op)
        return(id)
      }
    },
    getUploadOperation = function(jobId) {
      .operations$get(jobId)
    },
    onJobFinished = function(jobId) {
      .operations$remove(jobId)
    }
  )
)